Many thanks for your suggestions, I think as a newbie and specially if you start with Ubuntu, the security issue is not important for a while, after gain some experience using Fedora.
I changed Ubuntu to Fedora, 'cos I found many problems with driver compatibility specially if you're using an atheros wireless board. In Ubuntu sbin commands are available for all users. Nonetheless Fedora is stronger and more flexible and It has lots of potential for doing your own drivers!!